In recent years, triggered by a widespread use of DVDs or personal computers etc., there has been an increasing demand for image display devices which can handle image signals of different signal formats. For example, the image display devices which allow the input of both a component format signal having Y, Pb, and Pr signals and an analog RGB format signal including analog RGB signals and synchronization signals (H, V) have been growing in demand. Regarding to the component format, so-called a RCA terminal is typically used for inputting the signal, and for the analog RGB format, a D-Sub 15-pin terminal typically is used for inputting the signal.
Depending on the type of equipment connected to a device (such as commercial video display device), it is requested to employ a so-called BNC terminal instead of the above-mentioned terminals. In such a case, terminals for the component format and terminals for the analog RGB format can be provided separately. However, for reducing space on a substrate or a terminal strip, and for reducing a cost (by omitting terminals and a switching circuit), the Y, Pb, and Pr terminals for inputting a component format signal and G, B, and R terminals for inputting an analog RGB format signal may be shared. Such shared terminals used as input terminals adaptive for different signal formats are disclosed in, for example, JP-A-2004-21054 and JP-A-2007-241261.
According to the above-mentioned image display device having shared terminals, although it is advantageous in terms of reducing space, it is requested that the display can appropriately determine the signal format of an inputted image signal. This is because processing executed in the image display device differs between the image signal of the component format and of the analog RGB format.
One of the reason of the difference is that the image signal of the component format and of the analog RGB format are based on different standards regarding to the timing information of the signal, such as a dot clock or a front porch. Specifically, the timing information in the component format bases on the EIA (Electronic Industries Alliance) standard basically, whereas the timing information in the analog RGB format may base on wide variety of standards. Thus, it is difficult to pre-register timing information relating to various standards regarding to the analog RGB format in an image display device. Here, the timing information represents various timing information, such as a horizontal frequency, a vertical frequency, a dot clock, or a front porch, to which is referred in order to process image signals appropriately.
Further, in the analog RGB format, image signals conforming to an identical standard but different type (different in resolution, etc.) may be analogous in H (horizontal frequency) and V (vertical frequency) to one another in some cases. For example, as shown in Table 1, an image signals conforming to the VESA (Video Electronics Standards Association) standard with a resolution of 1024×768, 1366×768, 1360×768 and 1280×768 respectively, are analogous in H and V to one another.
TABLE 1Horizontal FrequencyVertical FrequencyResolutionH (KHz)V (KHz)1024 × 76848.3660.001366 × 76848.3660.011360 × 76847.7360.031280 × 76847.7859.87
Therefore when an image signal of the analog RGB format is inputted to the image display device, it may be difficult to identify its type among pre-registered timing information accurately, based on, H and V of the inputted image signal. Thus, in order to achieve an appropriate processing of the image signal, it is required that the content of identified timing information is adjustable afterwards.
On the other hand, when an image signal of the component format is inputted to the image display device, it is relatively easy to identify the timing information corresponding to the inputted image signal because since it is given that the image signal conforms to the EIA standard. Thus, the above-described adjustment of timing information is unnecessary, and further, when such adjustment is performed, it might cause a useless processing load. Further, in the EIA standard, H and V are not set similar between signals of different format, and thus the above-described identification is relatively easy.
Hence, the necessity of the adjustment of timing information differs depending on the signal format of the image signal inputted to an image display device. Furthermore, when an inputted image signal is in the component signal format, an appropriate image display is realized due to a display control based on a predetermined standard (preferably, the EIA standard).